The invention relates to an ultrasonic probe for non-destructive testing of metallic workpieces.
A generic ultrasonic probe is known from the utility model G 83 12 595.7. This probe consists of a linear array of oscillator elements which are arranged on a lead wedge made of Plexiglas. The wedge angle of the lead wedge is selected commensurate with the desired propagation direction of the soundwave in the workpiece.
Such probes are used, for example, to test pipes for transverse faults. The transverse fault test of pipes in the 12 o'clock position is a standard technique and is typically implemented by using two opposing probes which emit soundwaves in the direction of the respective other probe.
The probe pair includes either two angled probes or normal probes which couple soundwaves into the pipe at an angle, preferably through water coupling.
The pipe surface can be completely tested by moving the pipe, for example in a helical pattern, under the test unit arranged stationarily in the 12 o'clock position; alternatively, the pipe is rotated and the test unit moves linearly across the pipe surface.
To increase the test capacity of the fault test, e.g., for a rapid 100% test, additional probe pairs must be installed and arranged so as to enable testing of the workpiece surface without any gaps.
Because an arrangement of additional probe pairs in conjunction with a space-saving design frequently increases constructive expenditures, the multi-oscillator rulers (MFS rulers) known from the aforementioned utility model provide an attractive alternative.
MFS rulers are a plurality of ultrasound oscillators which are arranged closely spaced in a housing in form of a linear array, wherein the size of the oscillators depends on the type of the test to be performed.
So-called pulsed oscillators have been developed (DE 19860127 C1) to prevent gaps in the test which inherently unavoidable in this kind of test.
For the transverse fault test, the angle of incidence of the sound waves is maximally 70°, typically only 45°. Because MFS rulers are typically constructed as normal probes, the MFS ruler must be placed for angled incidence at an angle (angle of incidence) relative to the workpiece to be tested. This angle depends on the medium which has a specific sound velocity and can be calculated from the laws of refraction.
For example, the angle of incidence is small for media having low sound velocities, such as water.
Containers filled with water can be used without problem for ultrasound tests with MFS rulers if these containers are attached underneath the pipe (six o'clock test position).
Water containers for coupling are not feasible for a portal solution in a 12 o'clock test position due to the constructive complexity associated with sealing on the tested pipe.
Because the required seal, it is significantly easier to arrange the water containers and the test unit at the six o'clock position; however, the design prevents such an arrangement if the pipe to be tested must be movable on roller tables.
In these applications, the conventional lead wedges entirely made of plastic are typically used. Because of the higher sound velocity of plastic materials compared to water (about 50-100% higher), the wedge angle of the lead wedge is correspondingly greater. In addition to a greater installed height, which may cause constructive problems in some situations, greater wedge angles may also result in significantly longer sound propagation paths, which significantly reduce the echo amplitudes of the sound signal for the known greater damping in plastic compared to water, thus making reliable signal detection significantly more difficult or even impossible.
It is therefore an object of the invention to disclose an ultrasonic probe with a lead wedge and a multi-oscillator ruler for nondestructive testing for transverse faults of metallic workpieces, in particular of pipes, which also allow a simple and reliable ultrasound test on the workpiece in the 12 o'clock position, while simultaneously realizing a small overall height of the probe.